Method for supplying rotational speed signals

ABSTRACT

A method by which even if a plurality of devices requiring information in terms of the rotational speed of an engine or a wheel are installed in the same automobile, only one rotational speed detector for each phenomenon is employed to operate a plurality of devices requiring information in terms of the engine or wheel revolutions.

' United States Patent 1w] Araietal.

METHOD FOR SUPPLYING ROTATIONAL SPEED SIGNALS Inventors: Hiroshi Arai; Takakazu Mori, both of Toyoto, Japan Assignec: Toyota Jidosha Kogyo Kabushiki Kais ha, Toyota-shi, Japan Filed: March 24, 1971 Appl. No.: 127,650

Foreign'Application Priority Data April 2, 1970 Japan ...45/29127 U.S. Cl. ..307/l20, 324/174. 317/5 Int. Cl. ..H0lh 35/00 Field of Search ..324/173,174,171,163;

DETECTOR- 1451 Jan. 30, 1973 References Cited UNITED STATES PATENTS 3,358,230 12/1967 Wiley ..324/|7| Primary Examiner-Herman .I. Hohauser At!orney-Cushman, Darby & Cushrnan 57 ABSTRACT A method by which even ifa plurality of devices requiring information in terms ofthe rotational speed of an engine or a wheel are installed in the same automobile, only one rotational speed detector for each phenomenon is employed to operate a plurality of devices requiring information in terms of the engine or wheel revolutions.

4 Claims,4 Drawing Figures R07Z1770N4L e 0/ e5 METHOD FOR SUPPLYING ROTATIONAL SPEED SIGNALS BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates to a method for supplying rotational speed signals.

2. Description of the Prior Art Automotive vehicles have employed electrical devices which are designed to obtain information in termsof the rotational speed of the engine or the wheel, either to directly indicate such a rotational speed itself, or to take part in the control of the essential functions of the vehicles on the basis of such information. The former include, for example, a tachometer for indicating the rotative speed of an engine, a speedmeter for converting the rotational speed of a wheel into a circumferential speed to indicate the vehicles speed and an odometer for integrating the number of revolutions of a wheel to indicate the distance traveled, while the latter includes, for example, an automatic speed control system for providing a constant cruising speed control according to the vehicles speed, an electrical automatic transmission system which employs vehicle speed signals to determine the shift points of a hydraulic automatic transmission, and an anti-skid device for preventing locking of the wheels when the brakes are applied. Each of these devices requires a separately provided rotational speed detector, so that when two or more of these devices are required in combination on the same vehicle, the use ofsuch devices will be very uneconomical and undesirable since they need their own separate rotational speed detectors.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 illustrate some examples of the rotational speed detectors known in the art.

FIGS. 3 and 4 illustrate preferred embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 illustrating an example of the prior art rotational speed detectors, numeral 1 designates a pulse transducer comprising a permanent magnet 1a having a coil lb wound thereon and mounted on a shaft operatively associated with a rotating member whose rotational speed is to be detected, and the pulse transducer 1 is disposed opposite to a rotor 2 consisting of a toothed magnetic material which rotates at the same rpm or at a speed having a predetermined relation with the rotational speed of the rotating member, so that as the rotor 2 rotates, an AC current is generated by variations of the magnetic flux interlinking the coil lb. The alternating current generated by the pulse transducer 1 is applied to the base of a transistor 3 for amplification and the amplified alternating current is then applied to the base of a transistor 4. When the alternating current applied to the transistor 4 is negative, that is, when it has a polarity shown in FIG. 1 the transistor 4 is rendered conductive, while the transistor 4 is rendered non-conductive when the alternating current applied thereto is positive. Thus, for each cycle of the pulse transducer 1 a positive potential and a zero potential alternately appear at the collector of the transistor 4. Numeral 6 designates an operational amplifier whose output terminal is fed back to its inverting input terminal by way of a capacitor 8 to constitute an integrator. A capacitor 7 is charged (i.e., with a charging voltage e,) by way of a resistor 9 and a diode 10 when the transistor 4 is non-conductive, and when the transistor 4 is conducting this charging voltage is applied by way ofa diode 11 to the input terminal of the operational amplifier 6 to produce an output voltage at its output terminal. The voltage e, at the output terminal is given as where C, is the capacitance of the capacitor 7, C is the capacitance of the capacitor 8, and n is the number of times that the transistor 4 is rendered conductive. By suitably selecting the charging and discharging time constants of the capacitor 7, variations in the number of the teeth of the rotor 2 per unit time, i.e., its rotational speed can be detected in terms of an analog quantity.

FIG. 2 illustrates another example of the prior art rotational speed detectors in which a transistor 4 and the preceding component parts are identical in operation with the corresponding component parts illustrated in FIG. 1. A capacitor 12 and a resistor 13 constitute a differentiation circuit which conducts a transistor 14 by attaining the conduction level between the base and the emitter of the transistor 14 with the output obtainable when the collector voltage of the transistor 4 changes from a zero potential to a positive potential. In other words, each time the tooth of the rotor 2 passes through the pulse transducer 1, a pulse voltage appears at an output terminal e, of the transistor 14, so that the number of rotations of the rotor 2 can be detected in terms of a digital quantity. It is self-evident that by calculating the number of such pulses in terms ofa quantity per unit time, the device of the second example operates as a rotational speed detector. g r.

While the examples of the conventional rotative speed detectors have been described in which the rotational speed of a rotating member is detected in terms of an analog or digital quantity by means of a pulse transducer, there are many other'prior art rotational speed detectors such as one which detects the speed of an engine by virtue of variations in the voltage due to the closing and opening of the contact points of an engines distributor.

Referring now to FIG. 3, numerals 31 and 32 designate electrical devices shown in the form of blocks which require information in terms of the rotational speed of an engine or awheel. Numeral 20 designates a transistor whose base is connected to the output terminal of a rotational speed detector 30 and the transistor 20 is connected to constitute an emitter follower to reduce the output impedance. Numerals 2] and 22 designate diodes which apply'the analog or digital voltage, which is developed at the emitter of the transistor 20 and corresponds to the rotational speed, to the input terminals of the electrical devices 31 and 32, and which also serve to prevent the electrical devices 31 and 32 from interferring with each other by way of their input terminals. With this arrangement, it is no longer necessary to provide a separate rotational speed detector for each of the electrical devices. Instead, only one rotational speed detector is employed and an impedance transformer such as an emitter follower is connected to the output terminal of this detector, so that its output may be supplied as the required rotational speed information to the respective electrical devices by way of diodes provided to prevent mutual interference between the respective electrical devices.

Referring now to P10. 4 illustrating another embodiment of the present invention, numerals 31 and 32 designate electrical devices drawn in the form of blocks and requiring information in terms of the rotational speed of an engine or a wheel similarly with the electrical devices 31 and 32 shown in FIG. 3; 21' and 22' transistors whose bases are connected to the output terminal of a rotational speed detector 30 to constitute emitter followers to reduce the output impedance. The output terminals of the impedance transforming transistors 21' and 22 are connected to the input terminals of the electrical devices 31 and 32. This arrangement also makes it unnecessary to provide a separate rotational speed detector for each of the electrical devices, and the necessary rotational speed information can be supplied to the respective electrical devices by means of a single rotational speed detector.

Moreover, the embodiment of FIG. 4 is advantageous in that even if the voltage produced at the output terminal of the rotational speed detector 30 is an analog quantity and the electrical devices 31 and 32 need voltages of different values for a given rotational speed, the values of the biasing resistors or the load resistors may be set to any given values to meet the aforesaid requirement.

We claim:

1. A method for supplying electrical rotational speed signals to a plurality of electrical devices responsive thereto, comprising:

impedance transforming the electrical rotational speed signals to reduce the output impedance thereof, and coupling said transformed signals to at least one of said electrical devices in such a manner that said electrical devices are electrically separated from one another, whereby rotational speed signals are supplied independently to each of said plurality of electrical devices.

2. A supply circuit including rotational speed detector means adapted to provide electrical rotational speed signals and output devices responsive thereto comprising:

impedance transformer means having a reduced output impedance responsivel coupled to said speed detector means for trans ormmg the electrical speed signals through said reduced output impedance of said transforming means; and at least one of the output devices coupled to said impedance transformer means responsive to said transformed electrical signal, said output device electrically separated from any of the other electrical devices by means of said impedance transformer means. 3. The supply circuit of claim 2, wherein said impedance transformer is a diode.

4. The supply circuit of claim 2, wherein said impedance transformer is a transistor. 

1. A method for supplying electrical rotational speed signals to a plurality of electrical devices responsive thereto, comprising: impedance transforming the electrical rotational speed signals to reduce the output impedance thereof, and coupling said transformed signals to at least one of said electrical devices in such a manner that said electrical devices are electrically separated from one another, whereby rotational speed signals are supplied independently to each of said plurality of electrical devices.
 2. A supply circuit including rotational speed detector means adapted to provide electrical rotational speed signals and output devices responsive thereto comprising: impedance transformer means having a reduced output impedance responsively coupled to said speed detector means for transforming the electrical speed signals through said reduced output impedance of said transforming means; and at least one of the output devices coupled to said impedance transformer means responsive to said transformed electrical signal, said output device electrically separated from any of the other electrical devices by means of said impedance transformer means.
 3. The supply circuit of claim 2, wherein said impedance transformer is a diode.
 4. The supply circuit of claim 2, wherein said impedance transformer is a transistor. 